linux-stable.git/kernel/softirq.c, branch v5.2.1

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 430

2019-06-05T15:37:16+00:00

Based on 1 normalized pattern(s):

  distribute under gplv2

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 8 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Armijn Hemel 
Reviewed-by: Allison Randal 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190531190114.475576622@linutronix.de
Signed-off-by: Greg Kroah-Hartman

softirq: Remove tasklet_hrtimer

2019-03-22T13:36:02+00:00

There are no more users of this interface.
Remove it.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Anna-Maria Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Acked-by: David S. Miller 
Cc: netdev@vger.kernel.org
Link: https://lkml.kernel.org/r/20190301224821.29843-4-bigeasy@linutronix.de

softirq: Don't skip softirq execution when softirq thread is parking

2019-02-10T20:51:39+00:00

When a CPU is unplugged the kernel threads of this CPU are parked (see
smpboot_park_threads()). kthread_park() is used to mark each thread as
parked and wake it up, so it can complete the process of parking itselfs
(see smpboot_thread_fn()).

If local softirqs are pending on interrupt exit invoke_softirq() is called
to process the softirqs, however it skips processing when the softirq
kernel thread of the local CPU is scheduled to run. The softirq kthread is
one of the threads that is parked when a CPU is unplugged. Parking the
kthread wakes it up, however only to complete the parking process, not to
process the pending softirqs. Hence processing of softirqs at the end of an
interrupt is skipped, but not done elsewhere, which can result in warnings
about pending softirqs when a CPU is unplugged:

/sys/devices/system/cpu # echo 0 > cpu4/online
[ ... ] NOHZ: local_softirq_pending 02
[ ... ] NOHZ: local_softirq_pending 202
[ ... ] CPU4: shutdown
[ ... ] psci: CPU4 killed.

Don't skip processing of softirqs at the end of an interrupt when the
softirq thread of the CPU is parking.

Signed-off-by: Matthias Kaehlcke 
Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: "Paul E . McKenney" 
Cc: Sebastian Andrzej Siewior 
Cc: Douglas Anderson 
Cc: Stephen Boyd 
Link: https://lkml.kernel.org/r/20190128234625.78241-3-mka@chromium.org

Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2018-10-25T18:43:47+00:00

Pull irq updates from Thomas Gleixner:
 "The interrupt brigade came up with the following updates:

   - Driver for the Marvell System Error Interrupt machinery

   - Overhaul of the GIC-V3 ITS driver

   - Small updates and fixes all over the place"

* 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (31 commits)
  genirq: Fix race on spurious interrupt detection
  softirq: Fix typo in __do_softirq() comments
  genirq: Fix grammar s/an /a /
  irqchip/gic: Unify GIC priority definitions
  irqchip/gic-v3: Remove acknowledge loop
  dt-bindings/interrupt-controller: Add documentation for Marvell SEI controller
  dt-bindings/interrupt-controller: Update Marvell ICU bindings
  irqchip/irq-mvebu-icu: Add support for System Error Interrupts (SEI)
  arm64: marvell: Enable SEI driver
  irqchip/irq-mvebu-sei: Add new driver for Marvell SEI
  irqchip/irq-mvebu-icu: Support ICU subnodes
  irqchip/irq-mvebu-icu: Disociate ICU and NSR
  irqchip/irq-mvebu-icu: Clarify the reset operation of configured interrupts
  irqchip/irq-mvebu-icu: Fix wrong private data retrieval
  dt-bindings/interrupt-controller: Fix Marvell ICU length in the example
  genirq/msi: Allow creation of a tree-based irqdomain for platform-msi
  dt-bindings: irqchip: renesas-irqc: Document r8a7744 support
  dt-bindings: irqchip: renesas-irqc: Document R-Car E3 support
  irqchip/pdc: Setup all edge interrupts as rising edge at GIC
  irqchip/gic-v3-its: Allow use of LPI tables in reserved memory
  ...

softirq: Fix typo in __do_softirq() comments

2018-10-18T16:10:23+00:00

s/s/as

[ mingo: Also add a missing 'the', add proper punctuation and clarify what 'swap' means here. ]

Signed-off-by: Yangtao Li 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: alexander.levin@verizon.com
Cc: frederic@kernel.org
Cc: joel@joelfernandes.org
Cc: paulmck@linux.vnet.ibm.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/20181018142133.12341-1-tiny.windzz@gmail.com
Signed-off-by: Ingo Molnar

rcu: Define RCU-bh update API in terms of RCU

2018-08-30T23:02:40+00:00

Now that the main RCU API knows about softirq disabling and softirq's
quiescent states, the RCU-bh update code can be dispensed with.
This commit therefore removes the RCU-bh update-side implementation and
defines RCU-bh's update-side API in terms of that of either RCU-preempt or
RCU-sched, depending on the setting of the CONFIG_PREEMPT Kconfig option.

In kernels built with CONFIG_RCU_NOCB_CPU=y this has the knock-on effect
of reducing by one the number of rcuo kthreads per CPU.

Signed-off-by: Paul E. McKenney

rcu: Apply RCU-bh QSes to RCU-sched and RCU-preempt when safe

2018-08-30T23:02:38+00:00

One necessary step towards consolidating the three flavors of RCU is to
make sure that the resulting consolidated "one flavor to rule them all"
correctly handles networking denial-of-service attacks.  One thing that
allows RCU-bh to do so is that __do_softirq() invokes rcu_bh_qs() every
so often, and so something similar has to happen for consolidated RCU.

This must be done carefully.  For example, if a preemption-disabled
region of code takes an interrupt which does softirq processing before
returning, consolidated RCU must ignore the resulting rcu_bh_qs()
invocations -- preemption is still disabled, and that means an RCU
reader for the consolidated flavor.

This commit therefore creates a new rcu_softirq_qs() that is called only
from the ksoftirqd task, thus avoiding the interrupted-a-preempted-region
problem.  This new rcu_softirq_qs() function invokes rcu_sched_qs(),
rcu_preempt_qs(), and rcu_preempt_deferred_qs().  The latter call handles
any deferred quiescent states.

Note that __do_softirq() still invokes rcu_bh_qs().  It will continue to
do so until a later stage of cleanup when the RCU-bh flavor is removed.

Signed-off-by: Paul E. McKenney 
[ paulmck: Fix !SMP issue located by kbuild test robot. ]

nohz: Fix missing tick reprogram when interrupting an inline softirq

2018-08-03T13:52:10+00:00

The full nohz tick is reprogrammed in irq_exit() only if the exit is not in
a nesting interrupt. This stands as an optimization: whether a hardirq or a
softirq is interrupted, the tick is going to be reprogrammed when necessary
at the end of the inner interrupt, with even potential new updates on the
timer queue.

When soft interrupts are interrupted, it's assumed that they are executing
on the tail of an interrupt return. In that case tick_nohz_irq_exit() is
called after softirq processing to take care of the tick reprogramming.

But the assumption is wrong: softirqs can be processed inline as well, ie:
outside of an interrupt, like in a call to local_bh_enable() or from
ksoftirqd.

Inline softirqs don't reprogram the tick once they are done, as opposed to
interrupt tail softirq processing. So if a tick interrupts an inline
softirq processing, the next timer will neither be reprogrammed from the
interrupting tick's irq_exit() nor after the interrupted softirq
processing. This situation may leave the tick unprogrammed while timers are
armed.

To fix this, simply keep reprogramming the tick even if a softirq has been
interrupted. That can be optimized further, but for now correctness is more
important.

Note that new timers enqueued in nohz_full mode after a softirq gets
interrupted will still be handled just fine through self-IPIs triggered by
the timer code.

Reported-by: Anna-Maria Gleixner 
Signed-off-by: Frederic Weisbecker 
Signed-off-by: Thomas Gleixner 
Tested-by: Anna-Maria Gleixner 
Cc: stable@vger.kernel.org # 4.14+
Link: https://lkml.kernel.org/r/1533303094-15855-1-git-send-email-frederic@kernel.org

Mark HI and TASKLET softirq synchronous

2018-07-17T18:12:43+00:00

Way back in 4.9, we committed 4cd13c21b207 ("softirq: Let ksoftirqd do
its job"), and ever since we've had small nagging issues with it.  For
example, we've had:

  1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not deferred")
  8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do not get to run")
  217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")

all of which worked around some of the effects of that commit.

The DVB people have also complained that the commit causes excessive USB
URB latencies, which seems to be due to the USB code using tasklets to
schedule USB traffic.  This seems to be an issue mainly when already
living on the edge, but waiting for ksoftirqd to handle it really does
seem to cause excessive latencies.

Now Hanna Hawa reports that this issue isn't just limited to USB URB and
DVB, but also causes timeout problems for the Marvell SoC team:

 "I'm facing kernel panic issue while running raid 5 on sata disks
  connected to Macchiatobin (Marvell community board with Armada-8040
  SoC with 4 ARMv8 cores of CA72) Raid 5 built with Marvell DMA engine
  and async_tx mechanism (ASYNC_TX_DMA [=y]); the DMA driver (mv_xor_v2)
  uses a tasklet to clean the done descriptors from the queue"

The latency problem causes a panic:

  mv_xor_v2 f0400000.xor: dma_sync_wait: timeout!
  Kernel panic - not syncing: async_tx_quiesce: DMA error waiting for transaction

We've discussed simply just reverting the original commit entirely, and
also much more involved solutions (with per-softirq threads etc).  This
patch is intentionally stupid and fairly limited, because the issue
still remains, and the other solutions either got sidetracked or had
other issues.

We should probably also consider the timer softirqs to be synchronous
and not be delayed to ksoftirqd (since they were the issue with the
earlier watchdog problems), but that should be done as a separate patch.
This does only the tasklet cases.

Reported-and-tested-by: Hanna Hawa 
Reported-and-tested-by: Josef Griebichler 
Reported-by: Mauro Carvalho Chehab 
Cc: Alan Stern 
Cc: Greg Kroah-Hartman 
Cc: Eric Dumazet 
Cc: Ingo Molnar 
Signed-off-by: Linus Torvalds

softirq: Reorder trace_softirqs_on to prevent lockdep splat

2018-06-21T19:12:43+00:00

I'm able to reproduce a lockdep splat with config options:
CONFIG_PROVE_LOCKING=y,
CONFIG_DEBUG_LOCK_ALLOC=y and
CONFIG_PREEMPTIRQ_EVENTS=y

$ echo 1 > /d/tracing/events/preemptirq/preempt_enable/enable

[   26.112609] DEBUG_LOCKS_WARN_ON(current->softirqs_enabled)
[   26.112636] WARNING: CPU: 0 PID: 118 at kernel/locking/lockdep.c:3854
[...]
[   26.144229] Call Trace:
[   26.144926]  
[   26.145506]  lock_acquire+0x55/0x1b0
[   26.146499]  ? __do_softirq+0x46f/0x4d9
[   26.147571]  ? __do_softirq+0x46f/0x4d9
[   26.148646]  trace_preempt_on+0x8f/0x240
[   26.149744]  ? trace_preempt_on+0x4d/0x240
[   26.150862]  ? __do_softirq+0x46f/0x4d9
[   26.151930]  preempt_count_sub+0x18a/0x1a0
[   26.152985]  __do_softirq+0x46f/0x4d9
[   26.153937]  irq_exit+0x68/0xe0
[   26.154755]  smp_apic_timer_interrupt+0x271/0x280
[   26.156056]  apic_timer_interrupt+0xf/0x20
[   26.157105]  

The issue was this:

preempt_count = 1 << SOFTIRQ_SHIFT

	__local_bh_enable(cnt = 1 << SOFTIRQ_SHIFT) {
		if (softirq_count() == (cnt && SOFTIRQ_MASK)) {
			trace_softirqs_on() {
				current->softirqs_enabled = 1;
			}
		}
		preempt_count_sub(cnt) {
			trace_preempt_on() {
				tracepoint() {
					rcu_read_lock_sched() {
						// jumps into lockdep

Where preempt_count still has softirqs disabled, but
current->softirqs_enabled is true, and we get a splat.

Link: http://lkml.kernel.org/r/20180607201143.247775-1-joel@joelfernandes.org

Cc: Peter Zijlstra 
Cc: Ingo Molnar 
Cc: Linus Torvalds 
Cc: Mathieu Desnoyers 
Cc: Tom Zanussi 
Cc: Namhyung Kim 
Cc: Thomas Glexiner 
Cc: Boqun Feng 
Cc: Paul McKenney 
Cc: Masami Hiramatsu 
Cc: Todd Kjos 
Cc: Erick Reyes 
Cc: Julia Cartwright 
Cc: Byungchul Park 
Cc: stable@vger.kernel.org
Reviewed-by: Steven Rostedt (VMware) 
Fixes: d59158162e032 ("tracing: Add support for preempt and irq enable/disable events")
Signed-off-by: Joel Fernandes (Google) 
Signed-off-by: Steven Rostedt (VMware)